1. Field of the Invention
The present invention relates to semiconductor devices and methods for manufacturing semiconductor devices, and more particularly, is preferably applied to a method for forming oxynitride dielectric films.
2. Description of Related Art
There exists a known method for forming the gate dielectric film of a semiconductor device in a two-layer structure of an oxynitride film (oxide film including nitrogen) and an oxide film, in order to prevent boron contained in a P-type polysilicon gate from diffusing into the silicon substrate through the gate dielectric film and to thereby prevent the threshold voltage from changing.
In the method described above, an oxynitride film is formed by using nitrogen monoxide gas, at a temperature of 1000° C., for a duration of 20 seconds. Also, an oxide film is formed by wet oxidation with the flow rate of H2/O2=5 slm/slm, at a temperature of 850° C., for a duration of 3 minutes; alternatively, by dry oxidation with the flow rate of O2=2 slm, at a temperature of 1000° C., for a duration of 3 minutes.
Also, there is a known method for forming the gate dielectric film of a semiconductor device with an oxide film such as a SiO2 film, in order to form the gate dielectric film on a silicon substrate.
FIG. 7 is a cross-sectional view showing a conventional method for manufacturing a semiconductor device.
Referring to FIG. 7, a silicon substrate 11 is heat-treated with oxygen gas G12, to thereby form an oxide film 12 on the silicon substrate 11.
Also, in order to reduce the amount of gate leakage to the gate dielectric film, there is a method for forming the gate dielectric film with an oxynitride film (oxide film containing nitrogen) such as a SiON film.
FIG. 8 is a cross-sectional view indicating another example of a conventional method for manufacturing a semiconductor device.
Referring to FIG. 8, a silicon substrate 21 is heat-treated with dinitrogen monoxide gas G13, to thereby form an oxynitride film 22 on the silicon substrate 21.
Also, there exists a method of forming a gate dielectric film in a three-layer structure with an oxide film, an oxynitride film and an oxide film, in order to suppress generation of an interface state with the silicon substrate, and to reduce the amount of gate leakage to the gate dielectric film.